1. Technical Field
The present invention relates generally to locating systems and, more particularly, to a microwave or millimeter wave locating system for locating known features such as an airport runway and various features associated therewith, especially under conditions of low visibility.
2. Discussion
There exist a number of aircraft landing systems for guiding an aircraft to a safe landing when approaching a runway under conditions of low visibility. One known approach employs a ground controlled system which has a radar system with scanning antennas located near the runway. A ground operator is generally required to instruct the pilot of the aircraft of his position so that the pilot may adjust the position of the aircraft on approach of the desired landing path. Another approach is the instrument landing system (ILS) which employs antennas located near the runway which radiate a localization beam to provide left-right and up-down control guidance signals to a receiver in the aircraft. The receiver converts the guidance signals into meter pointer deflection signals which provide a pointer deflection for the pilot to fly the aircraft on the desired landing path. While these approaches have worked well, both have limited landing guidance capabilities. For instance, these approaches generally provide only one acceptable landing approach path and limited location information to the pilot.
More recently, microwave landing systems have been deployed for providing landing paths for an aircraft under conditions of low visibility. Conventional microwave landing systems generally employ a number of antennas located near the runway which scan the aircraft's approach region. Microwave receiving equipment is located on the aircraft which receives and decodes the scanning information and converts it to a display. However, the conventional microwave landing system typically provides a display which is significantly different from what the pilot would actually see. As a result, the conventional microwave landing system provides an image on a screen of the runway which the pilot relies on to guide the aircraft to the point where the runway becomes visible. At that point, the pilot typically relies on what he can see as the features that make up the conditions for landing and more easily manually land the aircraft visually.
Another approach is disclosed in U.S. Pat. No. 4,940,986 entitled "Millimeter Wave Locating" which discloses a number of millimeter wave sources located near runway light housings for radiating millimeter wave beams along the runway. An airborne millimeter wave camera is provided for receiving the signals and creating an image of the millimeter wave sources which corresponds substantially to a visible image perceived by a landing pilot. While this approach may provide the location of the runway, it generally does not provide narrow band receivers for sensing modulated signals which enable a pilot to more accurately locate other features and distinguish between such features. For instance, it is desirable for a pilot to accurately identify other ground and air features for purposes of crash avoidance. In addition, this approach does not allow a pilot to accurately distinguish between different types of features located on or near the runway.
It is therefore desirable to provide for a microwave or millimeter wave locating system which enables an operator to locate known features such as a runway and other selected features which may commonly be found on or near the runway. In addition, it is further desirable to provide for such a locating system which enables an operator to accurately distinguish between different types of located features. Furthermore, it is desirable to provide for narrow band detection of modulated signals so as to detect the location of the sources emitting the modulated signals.